In general, the present invention relates to vehicle testing. More particularly, the present invention relates to road testing a vehicle to measure tire performance. Most particularly, the present invention relates to isolating the forces on a tire as it is driven on an actual driving surface.
Tire testing is an important component in the ongoing pursuit of improved vehicle performance and safety. In this pursuit, many entities have attempted to measure performance characteristics of tires through the use of simulators and road testing.
Several examples of simulators are present in the art. Some of these simulators test a tire removed from the vehicle. Others test an entire vehicle and may analyze the performance of the vehicle""s tires during the simulation. Typically, in these simulators, the test vehicle is situated on an endless simulated driving surface that permits limited operation of the vehicle. Early simulators of this type relied on laterally fixed simulated surfaces such as roller beds or a pair of cylinders positioned under the vehicle""s tires allowing only straight-line testing of the vehicle without cornering.
To accommodate some cornering, one simulator has been provided with a widened test surface and lateral restraints that allowed limited lateral movement of the vehicle. Still another simulator has incorporated moveable track members that track the direction of the tire.
While advances have been systematically made in the simulator art, these devices still suffer from being costly, cumbersome, immobile, and insufficient for accurately replicating actual tire to driving surface contact. To accommodate an entire vehicle, the simulator must be large. This, in combination with the extensive controls and instrumentation used to monitor and manipulate the test vehicle, not only leads to a staggering cost of performing these tests, but it makes the simulator immobile. Thus, to perform testing on a test vehicle""s tire, the test vehicle must be brought to the simulator""s site, where it is tested without attention to the actual driving surfaces that the tire may be operated on.
On the subject of the tire-to-driving surface contact, most simulators are limited to the artificial surface presented by the belts or rollers. One simulator, however, has used textured belts to attempt to produce changes or variations in the simulated surface similar to those found during actual driving conditions. As will be appreciated, however, the textured belts cannot accurately match actual driving surfaces and the effects of weather on these surfaces.
To that end, road testing is often used to generate tire performance data on an actual driving surface. Test tires are equipped with transducers and driven on a test track to analyze their performance. During these tests, it is desirable to isolate the forces acting on the tire of a test vehicle. But, the test vehicle""s reaction to changes in the tractive forces caused by maneuvering prohibits true isolation of the forces on the tire. For instance, when measuring tire forces generated by cornering, as the tire is turned, the reactive forces at the tire change causing the vehicle to change direction. As a result, the vehicle reacts apart from the tire producing changes in weight distribution and suspension configuration among others. Similar changes in the vehicle""s dynamics occur during braking and acceleration. Under the forces caused by these actions, the weight distribution of the vehicle shifts between the tires. As a consequence, the tractive forces at the tires, measured by the tire transducers, are influenced by the movement of the vehicle during maneuvers. Thus, the change in the heading angle and load shift make it considerably more difficult to measure forces accurately at the tire.
One known device is capable of isolating the force on a tire. This device has been used to observe tire performance on different soils. In this device, a rail system has been constructed over a series of soil bins. The soil bins are essentially a series of containers formed by partitions in a long concrete channel. The rails are installed on either side of the channel along the top of the channel""s walls. The test vehicle is suspended from the rails allowing the tires to contact the soils within each bin. While the rails are capable of counteracting changes in vehicle dynamics caused by maneuvering actions, the enormity of this system makes it impractical from cost and mobility standpoints. Like the vehicle simulator art, the rail system is fixed and only allows testing at the testing facility.
In light of the existing art, it is an object of the present invention to produce a mobile method of testing a vehicle tire.
It is a further object of the present invention to present such a method of testing that improves the isolation of forces at the tire.
In view of at least one of these objects, the present invention provides a method for obtaining forces and moments at a tire of a test vehicle provided with a sensor for measuring the forces and moments, the method including coupling the test vehicle to an anchor vehicle having tractive forces greater than the test vehicles, wherein the coupling restricts the lateral, longitudinal, and yaw movement of the test vehicle relative to the anchor vehicle such that the anchor vehicle maintains the course and velocity of the test vehicle during testing; and performing dynamic testing of the test vehicle while the test vehicle is coupled to the anchor vehicle.
The present invention further provides a restrained vehicle dynamometer including a test vehicle coupled to an anchor vehicle such that the test vehicle is substantially restrained longitudinally, laterally, relative to the anchor vehicle and at least one sensor operatively engaging at least one tire of the test and in terms of yaw vehicle wherein the sensor is in communication with a controller.
The present invention further provides a method of testing a test tire on a test vehicle, the test vehicle having at least one sensor proximate the test tire for sensing forces and moments thereon, the method including coupling the test vehicle to an anchor vehicle such that the anchor vehicle is capable of maintaining the velocity and direction of the test vehicle, wherein the vehicles are coupled in substantially side-by-side relation to each other; locating the sensor proximate an outboard tire of the test vehicle; and performing dynamic testing of the test vehicle.